Problems arising from friction and wear on mechanical parts
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Friction is the phenomenon of mutual hindrance between the surfaces of relative moving objects.Friction can be divided into the following categories.Internal friction: the phenomenon occurring within a substance that prevents the relative motion of molecules.2. External friction: the phenomenon of mutual obstruction between the surfaces of relative moving objects.3. Static friction: friction with only relative motion trend.4, dynamic friction: friction in the process of relative motion.5. Sliding friction: the motion form between the surfaces of objects is relative sliding friction.Rolling friction: the motion form between the surfaces of objects is relative rolling friction.
Wear is the loss or transfer of materials on the surface of objects caused by friction. The research on wear was carried out relatively late. After the adhesion theory was put forward in the 1950s, in the 1960s, on the basis of the development of various surface analysis instruments, the research on wear was carried out rapidly.Wear is the friction between moving pairs which leads to the gradual loss or transfer of surface materials.Wear and tear will affect the efficiency of the machine, reduce the reliability of the work, to promote the early scrapping of the machine.
Mechanical wear can be roughly divided into three stages: running-in stage - new parts in the beginning of use generally in this stage;High wear rate;Stable wear stage -- belongs to the normal working stage of parts, with stable and low wear rate;Severe wear stage -- the stage when the parts are about to be scrapped, and the wear rate increases sharply.The three stages of wear are shown below:
According to the classification of wear mechanism, it can be generally summarized as follows: 1. Abrasive wear, referred to as wear, is the wear caused by free hard particles or hard contour peaks entering the friction surface from the outside; 2.2, fatigue wear, also known as pitting corrosion, is due to friction surface material microvolume under the action of alternating friction, repeated deformation of material fatigue caused by wear;3, adhesion wear, also known as agglutination, when the friction surface at every point of interaction between the contours of the peak due to the instantaneous temperature and pressure, after the "cold welding" in relative motion, material from a surface to another surface, it forms adhesion wear, 4, erosion wear and entrained in the flow of hard material or particles, in the friction surface under the action of a fluid impact caused by the wear and tear;5, corrosion wear, when the friction surface material in the chemical or electrochemical effect of the environment caused by corrosion, in the relative motion of the friction pair produced by the wear is corrosion wear;6. Fretting wear refers to the composite wear formed by the above mentioned wear mechanisms when the friction pair is in micro-motion. The micro-motion can be understood as the relative motion of the friction pair that is insufficient to make the abrasive particles break away.
Friction of mechanical parts is universal and unavoidable.Friction causes heat, temperature rise and energy loss, which leads to the loss and transfer of materials on the contact surface.Wear will damage the surface shape and size of parts, reduce the efficiency and reliability of machinery, until the loss of the original performance, type;To cause the wordy piece to be destroyed suddenly.At present, 1/3 ~ 1/2 of the energy in the industrial field in the world is finally consumed in various ways. About 80% of the damage of friction machinery parts is caused by various forms of wear.If we can try our best to reduce the useless friction consumption, we can save a lot of energy.In addition, the most vulnerable parts of mechanical products is due to wear and tear over limit scrapped and replaced, if can control and reduce the wear and tear, reduce maintenance frequency and cost, and can save the cost of the materials needed to manufacture parts and so how to do reduce the mechanical parts of the friction and wear are crucial for the development of industry and environmental protection.